These epidemiologic studies on heroin addiction in New York City will provide current information on the demographic characteristics and geographic distribution of addicts; the socio-economic factors associated with variations in rates of addiction, and the spread and extent of heroin addiction in the community. The M. J. Bernstein Institute of the Beth Israel Medical Center, New York, has been a major treatment center since 1961 and has cared for over 45,000 individual addicts. This project proposes intensive epidemiologic research of the addicts seen during 1970 for whom social and demographic data (directly comparable with the Federal Census) have been collected and who reside in five different areas of New York City. The spread of addiction within the Lower East Side of Manhattan in recent years will be studied in detail. Attention will be directed to developing improved estimates of the extent of narcotics addiction in New York City generally. These epidemiologic data are of prime relevance for planning and evaluation of treatment programs, as well as, elucidating some of the multiple social factors involved in the natural history of heroin addiction.